Loud speaker



Juiy 5, 1932. H. c. HOYT LOUD SPEAKER Filed Jul 3. 1930 anoemtoz Harald0.11091.

32,1, hi4 aum Patented July 5, 1932 I PATENT oFFlcE maom) 0. new, or'rnomas'ron, commc'rrcu'r 'LOUD SP AKER.

Application filed m a, 1930. Serial Nb. 465,567.

. 'This inventionrelates to'loud speakers of the dynamic type foramplifying electromagnetic vibrations received from phonographs, radios,talking picture films, andv other sources, and more particularly to animproved diaphragm for such a loud Speaker. One object ofthe'i'nventionis to provide a metallic loud speaker diaphragm of theabove nature which will be capable ofamplifying at high volume both highand low frequency vibrations.

' A further object is to provide a diaphragm of the above naturein whichundesired metallic sounds roduced by the natural period of thediapliragm are eliminated.

A further object is to provide a. device of the above nature which willbe simple in construction, lnexpensive to manufacture, easy to assembleand manipulate, compact, ornadurable in use. o I

With these and other objects in view there has been illustrated on theaccompanying drawing one form in which the invention may beconvenientlyembodied in practice.

In the drawing: l Fig.1 represents afront view of a dynamic loud speakerand diaphragm embodying the invention.

v Fig.2 is a transverse sectional viewof the same,taken along the line 22 ofFig. 1 look- 'ingdn the direction of the arrows. I

ig. 3 is a sectional 'view on an enlarged scale of one of thetri 0d armsof the loud speaker, taken along t e line 3.3 of Fig. 1, looking in thedirection of thearrows.

I Fig. 4 is a fragmentary sectional view on.

' an enlarged scale of the outer portion of the diaphragm and frame,taken along the line 4-4 of Fig. 1, looking in the direction of thearrows x q I In previous metal diaphragms for dynamic loud speakersconsiderable trouble has been experienced due to the undesired 'metallicvibration of the diaphragm itself. One method of avoiding; theseobjectionable I "sounds has been to stretch the metal' diaphragm so thatsaid natural period is of so higha pitch that the soundsproducedtheremental in appearance, and very efficient and ,sounds produced bythe'natural period of by will be inaudible. Thistypeof device, however,is very objectionable because owing to its highly stretched condition itwill not properly respond to the low frequency vibrations. Hence, whilehigh notes are radiated ina satisfactory manner, sounds of low pitch areradiated imperfectly. I I By means of the present invention, the aboveand other disadvantages have been overcome, and an electromagneticdiaphragm for a dynamic loud speaker has been pro: duced which will befree from undesirable sounds due to its natural period of vibration,

and at the same time will reproduce perfectly sounds of both high andlowfrequency over the entire audible range. Thishas been ac complishedby stretching the'metal of the diaphragm to a point .just underthenatural period of vibration, and absorbing the sounds due to saidnatural period by means of a ring of packing materiallocated under theouter periphery of the diaphragm, at which'point it has, been found thatsuch undesired sounds due tothe natural period of the metal arepractically all radiated.

To complete the manufacture of the diaphragm which would otherwise betoo elastic andwould cause an uneven response to the electromagneticimpulses of the driving coil and produce rattling and blurred and harsh,roaring: sounds at low frequencies under strong power, the presentinvention contemplates the attachment of' a plurality of thin dampingstrips to the inner surface of the metal diaphragm. The strips arepreferably I tangentially arranged with their inner edges overlapping,leaving an unsupported area at the central portion of the diaphragm.This stiffening of the outer'portionpf the diaphragm will permit it toradiate faithfully the low frequency vibrations while'the unstifi'enedcentral area thereof will, be free to radiate the high frequencyvibrations.

By means of a diaphragm made in accordance with the present invention,an accurate response will be obtained tovibrations ofall frequenciesfrom 30,000 .cycles per second at the highend of thescale down to'anydesired point on the low end of the scale, as

determined by the size of the diaphragm, the

weight of the driving coil and the thickness of the metal sheet.

Referring now to the drawing in which like reference numerals denotecorresponding parts throughout the several views, the numeral 10indicates a thin sheet metal diaphragm, preferably circular in shape.The diaphragm is preferably composed of aluminum alloy, such asduralumin or hard rolled aluminum.

The diaphragm sheet 10 is first laid with its outer edge located betweena pair of circular clamping bands 11 and 12, preferably constructed ofthe same metal as the diaphragm 10, so as to avoid uneven expansioneffects due to changes in temperature. The clamping bands 11 and 12,together with the diaphragm 10 held tightly therebetween, are thenplaced upon a ring shaped frame 13, substantially twice as large indiameter as the bands 11 and 12. The bands 11 and 12 are next bolted tosaid frame 13 by means of a plurality of studs 14, which desirably passthrough every other one of aseries of holes 15, spaced equally about thecircum- 1 ference of the frame 13.

In order to more securely clamp the bands 11 and 12 about the peripheryof the diaphragm. 10, additional screw bolts 16 are employed and arepassed through the other holes 15, alternating, with the studs 14. The

frame 13 and diaphragm 10 are adapted to be supported as a unit inspaced relation from the exciting coil, not shown, by three inclinedtripod legs 17, having transverse feet sections 18 adapted to beattached to the frame 13 as by screws 19. The tripod legs 17 are securedat their inner ends to a shouldered ring 20 which is shaped to fit thebase of said exciting field coil, not shown. a

After the diaphragm unit has been secured to the tripod legs 17, adamping, ring 21 of any suitable flexible packingematerial, such as.felt or cellucotton, is forced between the diaphragm 10 and the innerportions of the annular frame 13. This packing material serves to absorball metallic sounds or harmonies due to'vibrations in synchronism withthe natural period of the sheet metal.

The next step in the production of the improved loud speaker is tostiffen the outer portion; of the diaphragm. For this purpose,

a plurality" of. thin strips 22 of light material, such as balsa wood,are positioned in the tangential arrangement shown in Fig. 1,

being so placed as to form an unstiffened square central area 28-at thecenter of the diaphragm 10. The strips 22are preferably attached. to thediaphragm by rubber cement also by a row of stitching 24 of silk thread.sewed through the diaphragm, and consolidated. therewith by meansof acement containing a phenolic condensation product. The; strips 22zpermitthe diaphragm to accurately radiate the low frequency vibrations at theouter portion of said diaphragm. The central unstiffened portion of thediaphragm being fairly light and flexible and not requiring muchmovement, will accurately radiate all the high frequency vibrations.

In order to absorb any undesired resonance and metallic vibrations whichmight originate therein, each of said tripod legs 17 is madechannel-shaped in cross-secton and has its base 25 and inclined sides 26covered with a felt strip 27 adapted to be held in place by awedge-shaped strip of wood 28 secured to said base 25, as by screws 29.

It has been found that three of the tripod legs 17 are suflicient tohold the dynamic diaphragm unit in rigid position, but it will beunderstood that any other number of legs may be employed within thespirit of the invent-ion. The covering on the tripod legs 17 serves toprevent any resonance and me tallic sounds transmitted thereto by theframe work etc.

While there has been disclosed in thisspecification one form in whichthe invention ma be embodied, it is to be understood that this form isshown for the purpose of illustration only, and that the invention isnot to be limited to the specific disclosure but may be modified andembodied in various other forms cies under strong power, said diaphragm'having an unsupported central section for radiating sounds of low pitch,said strips being arranged in substantially radial overlapping positionstangent to said central section. 1 I 2. In a dynamic loudspeaker, ametal diaphragm, a frame surrounding said diaphragm, and a plurality ofstripsof balsa wood attached to said diaphragm for damping the vibrationof the outer part of said:

diaphragm to prevent radiation of undesired rattling and. roaring soundsof low frequencies under strong power, said diaphragm having anunsupported central section adapted to radiate low pitchsoundvibrations, said strips being arranged substantially radially aboutsaid central section.

3. In adynamic loudspeaker, a stretched metal diaphragm, a framesurrounding said diaphragm, and a plurality of strips attached to saiddiaphragm for damping the vibration of the outer partof said diaphragmto prevent radiation of undesired rattling and roaring sounds of lowfrequencies under strong power, said diaphragm havin an unsupportedcircularcentral section or radiating low pitch sound vibrations, saidstrips being located with their inner ends tangent to said unsupportedsection. v

4. In a d namic louds eaker, a stretched diaphragm aving an au iblenatural period of vibration, a frame surrounding said diaphragm, aplurality of strips for damping the vibration of the. outer part of saiddiaphragm to prevent radiation of undesired lasts, said diaphragm havinan unsuported circularcentral section or radiating 0w pitch soundvibrations, said strips bein located with their inner ends tangent tosai circular section.

5. In a dynamic loudspeaker, aframe for supporting the perifphery of athin metallic diaphragm, a ring or supportin a driving coil, a pluralityof inclined legs or connecting sai frame with-said ring, said legs beingcovered with sound absorbing material.

6. In a dynamic loudspeaker, a frame for supporting the periphery of athin metallic diaphragm, a rin or supportin a driving coil, a pluralityo inclined legs [or connecting said frame with said ring, each of saidlegs being channel-shaped and having a wedge member fitted within theopen side of said channel for sound-absorbing urposes.

7. In a dynamic loudspeaker, a rame for supporting the per fphery of athin metallic diaphragm, a ring or supporting a driving coil, aplurality of inclined legs or connecting said frame with said ring, eachof said legs being channel-shaped and having a wedge member fittedwithin the open side of said channel, and a strip of felt embracin saidchannel and being held in place by sai wedge member.

In testimony whereof, I have afiixed my signature to this specification.

HAROLD C. HOYT.

